This invention is related to the field of processes that produce polymers, where said polymers comprise polymerized ethylene. The phrase xe2x80x9cethylene polymersxe2x80x9d as used in this application includes homopolymers of ethylene, and copolymers of ethylene with another monomer. Particularly, this invention is related to the field of processes that produce ethylene polymers having a broad molecular weight distribution. More particularly, this invention is related to the field of processes that produce ethylene polymers that have low formation of smoke and odor during blow molding.
There are many production processes that produce ethylene polymers. Ethylene polymers are utilized in many products, such as, for example, films, coatings, fibers, bottles and pipe. Producers of such ethylene polymers are continuously conducting research to find improved ethylene polymers.
Ethylene polymers with a broad molecular weight distribution generally have excellent processing characteristics such as, for example, high shear ratio, high shear at onset of melt fracture, low weight and die swell, and excellent physical properties such as high environmental stress crack resistance. However, often times, these ethylene polymers can produce smoke and odors when blow molded into manufactures.
This invention provides ethylene polymers having a broad molecular weight distribution and also low formation of smoke and odors during blow molding. Due to these improved properties, these ethylene polymers are ideal for blow molding bottles and other manufactures.
It is an object of this invention to provide a process to polymerize ethylene, or to copolymerize ethylene with at least one other monomer, to produce ethylene polymers.
It is another object of this invention to provide said ethylene polymers.
It is another object of this invention to provide ethylene polymers having high environmental stress crack resistance and low formation of smoke and odor during blow molding.
It is yet another object of this invention to provide a process to use said ethylene polymers to produce a manufacture.
It is still yet another object of this invention to provide a manufacture comprising said ethylene polymers.
In accordance with this invention, a process is provided, said process comprising polymerizing ethylene, or copolymerizing ethylene with at least one other monomer, wherein said polymerizing is conducted:
in a loop reactor with isobutane as a diluent;
at a temperature in a range of about 200xc2x0 F. to about 220xc2x0 F.;
with a catalyst system comprising chromium and a support;
in the presence of at least one trialkylboron;
wherein the chromium is present in a range of about 1% by
weight to about 4% by weight based on the weight of the support;
wherein said support comprises silica and titania;
wherein said support has a surface area of about 400 m2/gram to about 800 m2/gram and a pore volume of about 1.8 ml/gram to about 4 ml/gram;
wherein the titania is present in a range of about 0.5% by weight to about 3% by weight titanium based on the weight of the support;
wherein said catalyst system is activated at a temperature from about 1000xc2x0 F. to about 1300xc2x0 F.;
wherein said trialkylboron is represented by the formula, BR3,
where R is an alkyl group of up to 12 carbon atoms.
In another embodiment of this invention, said ethylene polymers are provided.
In yet another embodiment of this invention, a process for using said ethylene polymers to produce a manufacture is provided.
In still another embodiment of this invention, a manufacture is provided comprising said ethylene polymers.
These and other objects of this invention will become more evident from the following description and claims.
A process comprising polymerizing ethylene, or copolymerizing ethylene with at least one other monomer is provided. Said xe2x80x9cat least one other monomerxe2x80x9d can be olefins having from 4 to about 16 carbon atoms per molecule. Suitable monomers, that can be polymerized with ethylene to produce copolymers with excellent properties, can be selected from the group consisting of 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene.
The polymerizing is conducted in a loop reactor process at a temperature in a range of about 200xc2x0 F. to about 220xc2x0 F. with isobutane as a diluent. The loop reactor process is well known in the art and is disclosed, for instance, in Norwood, U.S. Pat. No. 3,248,179, the disclosure of which is hereby incorporated by reference.
The polymerizing is conducted using a catalyst system comprising chromium and a support. The chromium can be any suitable chromium compound that facilitates the polymerization of olefins. Suitable examples of chromium compounds include, but are not limited to, chromium nitrate, chromium acetate, chromium trioxide, and mixtures thereof. The amount of chromium present is from about 1% by weight to about 4% by weight. Preferably, the amount of chromium present is from about 1.5% by weight to about 3.5% by weight, most preferably, from 2% by weight to 3% by weight, where such weight percents are based on the weight of the support.
The chromium can be combined with the support in any manner known in the art. Examples of combining the chromium with the support can be found in U.S. Pat. Nos. 3,976,632; 4,248,735; 4,297,460; and 4,397,766; the entire disclosures of which are hereby incorporated by reference.
The term xe2x80x9csupportxe2x80x9d is not meant to be construed as an inert component of the catalyst system. The support used in the catalyst system of this invention comprises (or alternatively, xe2x80x9cconsists essentially ofxe2x80x9d or xe2x80x9cconsists ofxe2x80x9d) silica and titania. These supports are known in the art and are disclosed in U.S. Pat. Nos. 2,825,721; 3,225,023; 3,226,205; 3,622,521; 3,625,864; 3,780,011; 3,887,494; 3,900,457; 3,947,433; 4,053,436; 4,081,407; 4,151,122; 4,177,162; 4,294,724; 4,296,001; 4,392,990; 4,402,864; 4,405,501; 4,434,243; 4,454,557; 4,735,931; 4,981,831; and 5,037,911, the entire disclosures of which are hereby incorporated by reference. However, it should also be noted that these supports are available commercially from such sources as the W. R. Grace Corporation.
Generally, the amount of titania present is from about 0.5% by weight to about 3% by weight titanium. Preferably, the amount of titania present is from about 0.8% by weight to about 2.6% by weight titanium, most preferably from 0.8% by weight to 1.5% by weight titanium, where such weight percents are based on the weight of the support.
The support has a surface area from about 400 m2/gram to about 800 m2/gram. Preferably, the support has a surface area from about 450 m2/gram to about 700 m2/gram, and most preferably, from 500 m2/gram to 600 m2/gram. Furthermore, the support has a pore volume of from about 1.8 ml/gram to about 4 ml/gram. Preferably, the support has a pore volume of from about 2 to about 3.5 ml/gram, and most preferably, from 2.3 ml/gram to 3 ml/gram.
The catalyst system used in this invention is activated in accordance with any manner known in the art that will contact an oxygen containing ambient with the catalyst system. Suitable examples of this type of procedure can be found in U.S. Pat. Nos. 3,887,494; 3,900,457; 4,053,436; 4,081,407; 4,296,001; 4,392,990; 4,405,501; and 4,981,831, the entire disclosures of which are hereby incorporated by reference. Generally, activation is conducted at a temperature in a range of about 1000xc2x0 F. to about 1300xc2x0 F. Preferably, activation is conducted at a temperature in a range of about 1050xc2x0 F. to about 1250xc2x0 F., and most preferably, from 1100xc2x0 F. to about 1200xc2x0 F. Currently, the preferred oxidizing ambient is air. This activation is carried out for a time period of about 1 minute to about 50 hours. This allows for at least a portion of any chromium in a lower valance state to be converted to a hexavalent state.
The polymerizing is also conducted in the presence of at least one trialkylboron with a formula, BR3, where R is an alkyl group of up to 12 carbon atoms. Preferably, said trialkylboron is triethylboron (TEB). The amount of the cocatalyst used in a polymerization, stated in parts per million by weight based on the weight of the diluent in the reactor, is from about 1 part per million to about 6 parts per million. Preferably, it is from about 1.5 parts per million to about 4 parts per million, and most preferably, it is from 2 parts per million to 3 parts per million.
Hydrogen can be present in the loop reactor to control molecular weight. Currently, about 0 to about 3 mole percent hydrogen can be used.
Generally, said ethylene polymers produced by this process have the following properties: a high load melt index (HLMI) of about 10 to about 60 grams per ten minutes; a density of about 0.950 to about 0.960 grams per cubic centimeter; a shear ratio (high load melt index (HLMI)/melt index (MI)) of about 100 to about 300, a polydispersity (weight average molecular weight (Mw)/number average molecular weight (Mn)) of about 15 to about 30; a Environmental Stress Crack Resistance (ESCR) (Condition A) of greater than 300 hours; xylene solubles of less than 1.0%; and a low molecular weight polymer content of less than 2%. Low molecular weight polymer is ethylene polymer with a molecular weight of less than 1000. Test methods to determine these properties are described subsequently in the Examples.
It is preferred when said ethylene polymers have a HLMI of about 15 to about 40 grams per ten minutes, and most preferably, 15 to 30 grams per ten minutes.
It is also preferred when said ethylene polymers have a density of about 0.952 to about 0.958 grams per cubic centimeter, and most preferably, 0.953 to 0.957 grams per cubic centimeter.
It is also preferred when said ethylene polymers have a shear ratio (HLMI/MI) of about 120 to about 200, most preferably, from 130 to 180.
It is also preferred when said ethylene polymers have a polydispersity (Mw/Mn) of about 18 to about 25, and most preferably, of 19 to 25.
It is also preferred when said ethylene polymers have a Environmental Stress Crack Resistance (Condition A) of greater than about 400 hours, and most preferably, greater than 500 hours.
It is also preferred when said ethylene polymers have a low formation of smoke and odor when blow molded into manufactures as indicated by having less than 0.85% xylene solubles and less than 1.6% low molecular weight polymer. Most preferably, said ethylene polymers have less than 0.6% xylene solubles and less than 1% low molecular weight polymer.
Said ethylene polymers can be used to produce manufactures. Said ethylene polymers can be formed into a manufacture by any means known in the art. For example, said ethylene polymers can be formed into a manufacture by blow molding, injection molding, and extrusion molding. Further information on processing said ethylene polymers into a manufacture can be found in MODERN PLASTICS ENCYCLOPEDIA, 1992, pages 222-298. One important application for said ethylene polymers is the production of bottles and other manufactures by blow molding.